Amendment Criteria of TAFs
Visibility
9000 meters = 56. miles
8000 meters = 5 miles (File IFR)
7000 meters = 4.3 miles
6000 meters = 3.7 miles
4800 meters = 3 miles
1600 meters = 1 mile Don't fly)
9999 means more than 6 miles visibility
Shortcut is to subtract 3 from the thousands place and call it miles.
Ceiling
If the forecast is Amend if...
No ceiling or ceiling above 3000' Forecast is not representative or ceiling is 3000' or less.
3000' to 2000' Ceiling = or < 3000' or below 2000'
Less than 2000' to 1000' = or < 2000' or below 1000'
Less than 1000' to 600' = or < 1000' or below 600'
Less than 600' to 200' = or < 600' or below 200'
Less than 200' = or < 200'
Visibility
Forecast Amend if:
< 5 miles Decreases to 5 miles or less
3 to 5 miles < than 5 or below 3 miles
2 to > 3 miles = or < 3 or below 2 miles
1 to > 2 miles = or < 2 or below 2 miles
1/2 to > 1 mile = or < 1 or below 1/2 mile
> 1/2 mile = or < 1/2 mile
Qualifying Terms of TAFs
LIFR (Low IFR)
Ceiling below 500' visibility below 1 mile
IFR
Ceiling 1000 to 500, visibility 1 to 3 miles
MVFR (Marginal VFR)
Ceiling 1000 to 3000, visibility 3-5 miles
VFR
Ceiling over 3,000, visibility over 5 miles
Intensity/proximity
- light, +heavy, no sign = moderate
VC: Vicinity 5-10 sm from runway center
Description
MI shallow, BC patches, DR drifting, TS Thunderstorm, PR Partial
BL blowing, SH showers, FZ freezing PO dust devil
Weather
DZ drizzle, RA rain, SN snow, SG snow grains
IC diamond dust, PE ice pellets, GR hail (French), GS small hail
Obscuration
BR mist (French), FG fog, FU smoke (French), VA volcanic ash
SA sand, HZ haze, SY blowing spray, DU dust PY spray
Other
SK sky clear CLR clear TCU towering cumulus
SQ squall, SS sand storm, DS dust storm, PO dust whirls
FC funnel cloud MI shallow SA sand
CAVOK = CAVU = WX NIL or SKC
CIG010 = ceiling 1000
SKY-X = sky partially obscured
9//005 Sky obscured(9), clouds not visible (//) 500' vertical visibility Octas (eights)
2CU030 = 2/8 scattered cumulus at 3000'
Prognostic TAF Qualifiers
Permanent shifts
GRADU = gradual change over 1/2 hour as with fog burning off
RAPID = with time a quick (less than 1/2 hour) turnabout
FRONT = rarely used
Short term variations
TEMPO = CHC less than 1 hour of variation
INTER = OCNL quick changes in ceilings/visibility
PROB = VRBL less certain of changes.
Others:
00000 = calm winds
VRB means variable direction of winds
1920 from 1900Z to 2000Z
OCNL, OCNLY = Occasional, occasionally means greater than 50% chance for less than half of the forecast period.
OTLK = outlook covers six hours following forecast period.
CHC = chance means 30 to 50% probability during forecast period.
SLGT CHC = 10 to 20% chance
ISOLD = isolated is lowest thunderstorm/precipitation alert level
WDLY SCT = widely scattered is less than 25% chance
SCT = scattered 25 to 54%
CHC means that there is a 30 to 50% likelihood of an event. Chance tests your appraisal of what is believable compared to what you would rather believe. Any flight into a chance of icing or thunderstorms is considered by the NTSB as an FAR violation.
NMRS = numerous is more than 54% chance
VCNTY = vicinity between 5 and 25 miles
VC-SHRA = rain showers in vicinity
NSW = no significant weather
9999 = visibility over 6 miles
BR = mist (baby rain)
T16/11 = temperature 16°C at 1100Z
6CU030 = 6/8th cumulus at 3000'
FEW = 1/8 to 2/8 sky coverage
COR = correction
SPECI = special or Special Report)
KPIT U.S. station identifiers begin with K followed by three letters.
201955Z 20th day 1955Z time of issue. It is always 6 digits and "Z"
COR for correction to observation) ...follows the time field (when present)?
RMK SLP013 remarks, sea level pressure 30.13
FM1930 FroM and 2-digit hour and 2-digit minutes indicates significant change in weather. Each FM group has a separate line which is indented five spaces.
PROB40 2022 PROBability and 2-digit percent; probable condition during 2-digit beginning and 2-digit ending time period.
Intensity or proximity
- = light no sign = moderate + = heavy
VC = vicinity This covers only weather in vicinity of airport up to ten miles.
TAFs tend to be more accurate than FAs.
Three FTs a day, valid for 24 hours
18 hour forecast with additional 6 a categorical outlook
Expected ceilings, clouds/coverage, visibility, weather, vision, surface winds
Outlook of last 6 hours is VFR, MVFR, IFR, and low IFR
Ceilings as C in 100s of feet above ground
Clouds in ascending order
Visibility in miles and fractions up to 2 miles. Over 6 not reported.
Winds reported to neared 10 degrees from true north in knots.
Extends only 5 miles from airport center
VCTNY in forecast means within 25 miles
Never use an FT after the station has closed for the day.
If the surface report and FT are not available at destination have alternate.
2/10 of weather coverage (rain) means that 80% of area is rain free.
When METAR data is missing from the body of the report (e.g. dew point), it is simply omitted and the user must know the sequence to recognize this. Some exceptions apply in remarks such as RVRNO, or SLPNO when RVR or SLP are normally reported but not currently available. METARs exclude trend forecast.
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